As of the end of each calendar year, the increase in the ratio of the Consumer Price Index to the index as of the prior December thirty-first must be determined, and if the increase equals or exceeds four percent, the retirement allowance, inclusive of the supplemental allowances payable under the provisions of Sections 9-1-1910, 9-1-1920, and 9-1-1930, of each beneficiary in receipt of an allowance must be increased by four percent. If the increase in the index is less than four percent, the retirement allowance, inclusive of supplemental allowances, all as determined above, must be increased by a percentage equal to the increase in the index. The increase in retirement allowances commences the July first immediately following the December thirty-first that the increase in ratio was determined, and all increases in retirement allowances must be granted to these beneficiaries in receipt of a retirement allowance on July first immediately preceding the effective date of the increase. Any increase in allowances is effective only if the additional liabilities because of the increase in allowances do not require an increase in the total employer rate of contribution. Any increase in allowance granted pursuant to this section must be included in the determination of any subsequent increases, irrespective of any subsequent decrease in the Consumer Price Index.

The allowance of a surviving annuitant of a beneficiary whose allowance is increased under this section must, when and if payable, be increased by the same percent.

For purposes of this section,"Consumer Price Index" means the Consumer Price Index for Wage Earners and Clerical Workers, as published by the United States Department of Labor, Bureau of Labor Statistics.